The most common cause is using the wrong username and password. Make sure in Outlook you have it set with your full email address as the username. For the password, it's the password for that individual email account. Once the user information's confirmed, try sending a new email and see if the error is gone.

Sometimes this is caused by the Outgoing Server using the wrong port number. Please read our article on correcting sending email errors to make sure the right port is used. If this is a recent problem, it's possible your ISP blocked the port you're using. This can be corrected by simply changing the port as the article above recommends.

This error also occurs if a recently updated firewall or virus protector is blocking the email. To test this, temporarily lower your security settings and attempt to send an email. If you can, then the anti-virus is the likely issue.

If none of these work, our support team can look into the issue further. If you are able to, forward a screenshot of the error you're seeing to
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. Remember that you can always log into webmail to continue checking and sending email as well.

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Thank you for contacting. Have you tried on a different network? For example, if you are on a home network, try to transmit from a school, coffee shop, or library. This will help rule out network limitations.

If you were hosted on our servers, the next step is reviewing your mail logs for additional errors/issues. Unfortunately, since your email is with yahoo, we do not have access these logs. Have you tried to contact Yahoo support regarding this issue?